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  <title>用回调函数迭代地将数组简化为单一的值</title>
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  <div id="layout-content"><div id="function.array-reduce" class="refentry">
 <div class="refnamediv">
  <h1 class="refname">array_reduce</h1>
  <p class="verinfo">(PHP 4 &gt;= 4.0.5, PHP 5, PHP 7, PHP 8)</p><p class="refpurpose"><span class="refname">array_reduce</span> &mdash; <span class="dc-title">用回调函数迭代地将数组简化为单一的值</span></p>

 </div>
 <div class="refsect1 description" id="refsect1-function.array-reduce-description">
  <h3 class="title">说明</h3>
  <div class="methodsynopsis dc-description">
   <span class="methodname"><strong>array_reduce</strong></span>(<span class="methodparam"><span class="type">array</span> <code class="parameter">$array</code></span>, <span class="methodparam"><span class="type"><a href="language.types.callable.html" class="type callable">callable</a></span> <code class="parameter">$callback</code></span>, <span class="methodparam"><span class="type"><a href="language.types.declarations.html#language.types.declarations.mixed" class="type mixed">mixed</a></span> <code class="parameter">$initial</code><span class="initializer"> = <strong><code>null</code></strong></span></span>): <span class="type"><a href="language.types.declarations.html#language.types.declarations.mixed" class="type mixed">mixed</a></span></div>

  <p class="para rdfs-comment">
   <span class="function"><strong>array_reduce()</strong></span> 将回调函数
   <code class="parameter">callback</code> 迭代地作用到
   <code class="parameter">array</code> 数组中的每一个单元中，从而将数组简化为单一的值。
     </p>
 </div>

  <div class="refsect1 parameters" id="refsect1-function.array-reduce-parameters">
  <h3 class="title">参数</h3>
  <p class="para">
   <dl>
    
     <dt>
<code class="parameter">array</code></dt>

     <dd>

      <p class="para">
       输入的 array。
      </p>
     </dd>

    
    
     <dt>
<code class="parameter">callback</code></dt>

     <dd>

      <div class="methodsynopsis dc-description">
       <span class="methodname"><span class="replaceable">callback</span></span>(<span class="methodparam"><span class="type"><a href="language.types.declarations.html#language.types.declarations.mixed" class="type mixed">mixed</a></span> <code class="parameter">$carry</code></span>, <span class="methodparam"><span class="type"><a href="language.types.declarations.html#language.types.declarations.mixed" class="type mixed">mixed</a></span> <code class="parameter">$item</code></span>): <span class="type"><a href="language.types.declarations.html#language.types.declarations.mixed" class="type mixed">mixed</a></span></div>

    <dl>
    
     <dt>
<code class="parameter">carry</code></dt>

     <dd>

      <p class="para">
        携带上次迭代的返回值；
       如果本次迭代是第一次，那么这个值是 <code class="parameter">initial</code>。
      </p>
     </dd>

    
     
        <dt>
<code class="parameter">item</code></dt>

        <dd>

         <p class="para">
           携带了本次迭代的值。
         </p>
        </dd>

       
   </dl>

     </dd>

    
    
     <dt>
<code class="parameter">initial</code></dt>

     <dd>

      <p class="para">
       如果指定了可选参数
   <code class="parameter">initial</code>，该参数将用作处理开始时的初始值，如果数组为空，则会作为最终结果返回。
      </p>
     </dd>

    
   </dl>

  </p>
 </div>

 <div class="refsect1 returnvalues" id="refsect1-function.array-reduce-returnvalues">
  <h3 class="title">返回值</h3>
  <p class="para">
   返回结果值。
  </p>
  <p class="para">
   如果数组为空，并且没有指定
   <code class="parameter">initial</code> 参数，<span class="function"><strong>array_reduce()</strong></span> 返回 <strong><code>null</code></strong>。
  </p>
 </div>



 <div class="refsect1 changelog" id="refsect1-function.array-reduce-changelog">
  <h3 class="title">更新日志</h3>
  <table class="doctable informaltable">
   
    <thead>
     <tr>
      <th>版本</th>
      <th>说明</th>
     </tr>

    </thead>

    <tbody class="tbody">
     <tr>
 <td>8.0.0</td>
 <td>
  如果 <code class="parameter">callback</code> 接受引用传递参数，该方法将会抛出
  <strong><code>E_WARNING</code></strong>。
 </td>
</tr>

    </tbody>
   
  </table>

 </div>


 <div class="refsect1 examples" id="refsect1-function.array-reduce-examples">
  <h3 class="title">范例</h3>
  <p class="para">
   <div class="example" id="example-4946">
    <p><strong>示例 #1 <span class="function"><strong>array_reduce()</strong></span> 例子</strong></p>
    <div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB">&lt;?php<br /></span><span style="color: #007700">function&nbsp;</span><span style="color: #0000BB">sum</span><span style="color: #007700">(</span><span style="color: #0000BB">$carry</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">$item</span><span style="color: #007700">)<br />{<br />&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="color: #0000BB">$carry&nbsp;</span><span style="color: #007700">+=&nbsp;</span><span style="color: #0000BB">$item</span><span style="color: #007700">;<br />&nbsp;&nbsp;&nbsp;&nbsp;return&nbsp;</span><span style="color: #0000BB">$carry</span><span style="color: #007700">;<br />}<br /><br />function&nbsp;</span><span style="color: #0000BB">product</span><span style="color: #007700">(</span><span style="color: #0000BB">$carry</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">$item</span><span style="color: #007700">)<br />{<br />&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="color: #0000BB">$carry&nbsp;</span><span style="color: #007700">*=&nbsp;</span><span style="color: #0000BB">$item</span><span style="color: #007700">;<br />&nbsp;&nbsp;&nbsp;&nbsp;return&nbsp;</span><span style="color: #0000BB">$carry</span><span style="color: #007700">;<br />}<br /><br /></span><span style="color: #0000BB">$a&nbsp;</span><span style="color: #007700">=&nbsp;array(</span><span style="color: #0000BB">1</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">2</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">3</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">4</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">5</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">$x&nbsp;</span><span style="color: #007700">=&nbsp;array();<br /><br /></span><span style="color: #0000BB">var_dump</span><span style="color: #007700">(</span><span style="color: #0000BB">array_reduce</span><span style="color: #007700">(</span><span style="color: #0000BB">$a</span><span style="color: #007700">,&nbsp;</span><span style="color: #DD0000">"sum"</span><span style="color: #007700">));&nbsp;</span><span style="color: #FF8000">//&nbsp;int(15)<br /></span><span style="color: #0000BB">var_dump</span><span style="color: #007700">(</span><span style="color: #0000BB">array_reduce</span><span style="color: #007700">(</span><span style="color: #0000BB">$a</span><span style="color: #007700">,&nbsp;</span><span style="color: #DD0000">"product"</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">10</span><span style="color: #007700">));&nbsp;</span><span style="color: #FF8000">//&nbsp;int(1200),&nbsp;因为：10*1*2*3*4*5<br /></span><span style="color: #0000BB">var_dump</span><span style="color: #007700">(</span><span style="color: #0000BB">array_reduce</span><span style="color: #007700">(</span><span style="color: #0000BB">$x</span><span style="color: #007700">,&nbsp;</span><span style="color: #DD0000">"sum"</span><span style="color: #007700">,&nbsp;</span><span style="color: #DD0000">"No&nbsp;data&nbsp;to&nbsp;reduce"</span><span style="color: #007700">));&nbsp;</span><span style="color: #FF8000">//&nbsp;string(17)&nbsp;"No&nbsp;data&nbsp;to&nbsp;reduce"<br /></span><span style="color: #0000BB">?&gt;</span>
</span>
</code></div>
    </div>

   </div>
  </p>
 </div>

  <div class="refsect1 seealso" id="refsect1-function.array-reduce-seealso">
  <h3 class="title">参见</h3>
  <p class="para">
   <ul class="simplelist">
    <li class="member"><span class="function"><a href="function.array-filter.html" class="function" rel="rdfs-seeAlso">array_filter()</a> - 使用回调函数过滤数组的元素</span></li>
    <li class="member"><span class="function"><a href="function.array-map.html" class="function" rel="rdfs-seeAlso">array_map()</a> - 为数组的每个元素应用回调函数</span></li>
    <li class="member"><span class="function"><a href="function.array-unique.html" class="function" rel="rdfs-seeAlso">array_unique()</a> - 移除数组中重复的值</span></li>
    <li class="member"><span class="function"><a href="function.array-count-values.html" class="function" rel="rdfs-seeAlso">array_count_values()</a> - 统计数组中所有的值</span></li>
   </ul>
  </p>
 </div>

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